(a) Field
The described technology relates to a transmission control method. More particularly, the described technology relates to a transmission control method in a wireless local area network (WLAN).
(b) Description of the Related Art
A WLAN is being standardized by the IEEE (Institute of Electrical and Electronics Engineers) Part 11 under the name of “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.”
After an original standard was published in 1999, new version standards are continuously published by amendments. The IEEE standard 802.11a (IEEE Std 802.11a-1999) supporting 5 GHz band and the IEEE standard 802.11b (IEEE Std 802.11b-1999) supporting 2.4 GHz band were published in 1999, and the IEEE standard 802.11g (IEEE Std 802.11g-2003) supporting 2.4 GHz band was published in 2003. These standards are called legacy. Subsequently, the IEEE standard 802.11n (IEEE Std 802.11n-2009) for enhancements for higher throughput (HT) was published in 2009, and the IEEE standard 802.11ac (IEEE 802.11ac-2013) for enhancements for very high throughput (VHT) was published in 2013. Hereinafter, a WLAN supporting the legacy standard is referred to a “legacy WLAN,” a WLAN supporting the HT standard is referred to as an “HT WLAN,” and a WLAN supporting the VHT standard is referred to as a “VHT WLAN.”
In wireless communication networks such as the WLAN, each device occupies resources using a contention-based access scheme and transmits a signal. The WLAN device uses a carrier sense multiple access (CSMA) protocol to avoid collisions. In the CSMA protocol, the WLAN device detects energy on a channel and transmits the signal only when the channel is not being used. If the detected energy is above a clear channel assessment (CCA) threshold, the WLAN device deems that the channel is busy and performs a CCA operating for deferring the transmission attempt.
Recently, the IEEE 802.11ax task group has been developing a high efficiency (HE) WLAN for enhancing the system throughput in high density scenarios. In high density scenarios, a certain basic service set (BSS) may have a neighbor basis service BSS neighboring to it. In this, the WLAN device may lose its transmission opportunity during a transmission time of the neighbor BSS by performing the CCA operation according to a signal received from the neighbor BSS.
As such, since the WLAN may loss the transmission opportunity by the signal transmission of the neighbor BSS although a signal is not transmitted in its BSS, a channel cannot be efficiently used.